1. Field of the Invention
This invention relates to a drive apparatus for a cross-coil type meter having a magnet rotor and a pair of cross coils which are disposed in such a way that one is positioned at an angle with respect to the other, the magnetic field set up by cross coils causes the magnet to rotate, and measurement is displayed in terms of the rotational angle of the magnet rotor.
2. Description of Prior Art
Japanese Patent publication No. 62-16381 discloses one such type of conventional drive apparatus. A pair of coils are disposed to intersect at a right angle with respect to each other and a pointer is located at the intersecting point of the two coils. The pair of coils set up a magnetic field that causes a pointer to point an angular position in octants. Eight consecutive octants constitute a complete rotation (360 degrees in total) of the shaft or a magnet rotor. A drive current having a variable duty cycle in the range from 0 to 100% is allowed to flow through one of the coils in accordance with a quantity to be measured, while a current equal to the maximum value of the drive current is allowed to flow through the other coil, thereby determining an angular position of the pointer in an octant of the rotation of the magnet rotor. Thus the magnet rotor rotates an angle in accordance with the quantity to be measured so that the one can tell the measurement in terms of the angular position of the pointer. Selecting the polarity of the currents through the cross coils permits the pointer to deflect in a specified octant out of eight octants.
The above-mentioned prior art drive apparatus suffers from problems that a logic circuit for determining an octant in which the pointer is to deflect is of complexity as well as a pointer-zero-returning device such as a magnet or a hair spring etc. cause errors in indication since a unit drive current is assumed to accurately produce a unit angular positional displacement of the pointer. The present invention was made to overcome the aforementioned drawbacks.